Question

Running on a treadmill is slightly easier than running outside because there is no drag force to work against. Suppose a 60 kg runner completes a 5.0 km race in 20 minutes. Determine the drag force on the runner during the race. Suppose that the cross section area of the runner is 0.72 m

Answer 1

Answer:

The answer is 5.7 N

Step-by-step explanation:

m r  =  60  k g

d  =  5.0  k m =  5000 m  Distance covered by the runner

t  =  23 m i n  x 60 s/ 1 m i n = 1380 s

Time it the runner to complete the race

Cross-sectional area of the runner   A = 0.72   m^2

Coefficient of drag of a standing person  (C D)  = 1.0

Air density  ρ  =  1.2 k g /m^ 3  

The formula of drag force is F  =  CDA ρV2/2

Now find the speed by time and distance

speed (v) = Distance / time

               = 5000 m/1380 s = 3.623 m/s

Now solve for the drag force.

F = CDA ρV2/2 = 1.0 x (0.72 m^2)(1.2) (3.623)/2

                          = 5.7 N

Thus the drag force on the runner is 5.7 N